Tools can be inserted into process fluid flowing through the flow lines such as thermowells, injection quills, and sensor probes. A thermowell has a body with a closed end that is inserted into the process fluid and an open end, and the body defines an interior cavity (e.g., cylindrical cavity) that starts prior to the closed end and terminates at the open end. A temperature sensor can be inserted into the interior cavity to measure the temperature of the process fluid flowing through the flow line. An injection quill is a hollow cylinder with two open ends that allows a second fluid to be injected into the process fluid stream. A sensor probe is a cylindrical probe that is placed into a process stream. The sensor probe may be configured to measure temperature, flow, or another process parameter.